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Tech Notes

Published by: Larry Bloomfield & Jim Mendrala

(408) 778-3412 or (661) 294-1049

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August 16, 1999

Tech Note - 037


Talent does what it can, but genius does what it must!

Our Mission: Sharing experiences, knowledge, observations, concerns, opinions or anything else relating to Electronic Cinema, DTV, etc., with fellow engineers and readers. We do hope that everyone will participate with comments, experiences, questions and/or answers.  The other stuff that used to be up here is now at the end of this newsletter.  We now have over 440 subscribers and growing.  This is YOUR forum! 

                                   Past issues are available at: WWW.SCRI.COM


Subj: Performance Comparison of ATSC 8-VSB and DVB-T COFDM Transmission

Systems for Digital Television Terrestrial Broadcasting

By: Dr. Yiyan Wu - Communications Research Centre Canada

3701 Carling Avenue, Ottawa, Canada K2H 8S2

(Ed NoteThe following is presented a one position from a very heated debate currently going on in the industry.  Tech Notes presents it in an effort to present a well rounded points of view.)


This paper compares the performances of ATSC 8-VSB and DVB-T COFDM transmission systems for Digital Television Terrestrial Broadcasting. The comparison is based on the most recent laboratory test results and theoretical analysis.

1. Introduction

After a decade of intense research and development, Digital Television Terrestrial Broadcasting (DTTB) has finally reached the point of implementation stage. DTTB services have been available in North America and Europe, since November 1998. Many countries have announced their choice for a DTTB system and their implementation plan.

There are two very different digital modulation techniques used in DTTB systems: the Trellis Coded 8-Level Vestigial Side-Band (8-VSB) modulation system developed by the

Advanced Television Systems Committee (ATSC); and the Coded Orthogonal Frequency Division Multiplexing (COFDM) modulation adopted in the Digital Video Terrestrial Broadcasting (DVB-T) standard. Another DTTB transmission system, also based on COFDM, the Bandwidth Segmented Transmission (BST)-OFDM system for Terrestrial Integrated Service Digital Broadcasting (ISDB-T), has recently been finalized in Japan. Since there are more than one DTTB systems, many countries and administrations are now engaged in the process of selecting a DTTB system. Each country has specific characteristics and needs. The selection of a DTTB system must be based upon how well each of the modulation systems meets specific conditions such as spectrum resource, policy, coverage requirements and network structure, reception conditions, type of service required, objectives for program exchange, cost to the consumers and broadcasters, etc. This paper compares the performances of the ATSC 8-VSB and the DVB-T COFDM transmission systems under different impairments and operating conditions. First, a general system level comparison is presented. It is followed by the comparison of the most up-to-date laboratory test results and theoretical analysis. The differences in the system threshold definitions are discussed. A calculated fair performance comparison of 8-VSB and COFDM is provided. The 6, 7 and 8 MHz version of systems should exhibit the same performance, since identical modulation and channel coding schemes are used. In addition, a brief performance and implementation analysis is also presented for the two modulation systems under different network infrastructures. Whenever possible, the impact on the broadcasters or consumers are discussed. Possible performance improvements are indicated. It should be pointed out that both systems are working systems and are already providing viable DTV services.

However, the performance benchmarks quoted in this paper only indicate current technologies. Meanwhile, the tests have been conducted in different laboratories, under different test environments and using receivers from different manufacturers over more than one generation of products. Some minor differences are likely to appear. On the other hand, with the technical advances, both systems will achieve some performance improvements.

2. General System Comparison

Generally speaking, each system has its own unique advantages and disadvantages. The ATSC 8-VSB system is more robust in an Additive White Gaussian Noise (AWGN) channel, has a higher spectrum efficiency, a lower peak-to-average power ratio, and is more robust to impulse noise and phase noise. It also has comparable performance to DVB-T on low level ghost ensembles and analog TV interference into DTV. Therefore, the ATSC 8-VSB system could be more advantageous for Multi-Frequency Network (MFN).


Subj: DTV Measurements Seminar

By:  Larry Bloomfield

Know anyone at Hewlett Packard?  If you do and you'd like to attend the latest in their DTV Measurements Seminars, get to a callin!  According to the press on this, "TV engineering managers, transmitter engineers, field engineers and technicians, production engineers, and sales engineers who are responsible for digital signal quality and adherence to FCC performance standards will find this seminar helpful." 

HP says that digital Television (DTV) signals require new ways to measure quality of service, troubleshoot problems and ensure Federal Communication Commission (FCC) compliance. So, if you're responsible for addressing these issues, you need a solid understanding of these measurements and how to make them in order to be successful. This seminar is targeted at presents the basics of digital TV measurements and give the attendees the opportunity to gain hands-on experience using solutions that can help you deliver a quality DTV signal, resolve DTV problems and meet FCC requirements. If possible, a live local digital TV signal is also evaluated.

The seminar format is designed to provide useful information in an easy-to-grasp manner through presentations, demonstrations and an opportunity to see and operate some of HP's digital television measurement solutions. You will leave the seminar with a better understanding of the basics of digital television measurements, the tools necessary to meet expanding job responsibilities, HP solutions for television stations and a comprehensive seminar workbook.

All sessions are slated to begin at 10 AM and will condlude at 1:30 pm with a Hands-on Lab.   The tour will begin in San Francisco on August 31st and end, after a nation wide tour, in Phoenix, AX on October 29th.  Your local HP Measurements can provide you with exact locations and dates.  Don't delay as the seminar is filling up fast.


Subj: DTV reception in San Francisco / San Carlos

By:  Adam Wilt >>>  <<<

(Ed NoteThis information is shared for your information, with the authors permission as it was reprinted  from another forum.  It appears to be typical of what's going on elsewhere)

Some recent observations / tests in the San Francisco DTV mosh pit:

1) Eber Electronics is an AV retailer on Market Street in San Francisco, a mile or two away from the DTV antenna on Sutro Tower. If you step out the door and turn 90 degrees left, there it is.

Eber has the new Sony Wega HTDV set with Sony 8VSB receiver incorporated. It demos using a set-top rabbit ears antenna. Analog is received with no problem (most the analog transmitters for local stations are also beaming off of Sutro Tower, as are all the DTV transmitters). DTV reception is marginal; passing streetcars or big trucks will cause momentary losses or blocking of the picture.

2) Last night a chief engineer for one of the local stations came by friend's house in San Carlos (all people and product names deleted by request) to test out DTV reception with a prototype "2nd generation" STB due on the market in a couple of months.

The location is about 25 miles from Sutro Tower, and is blocked from direct line of sight by the coastal hills. Were we to levitate about 1000 feet higher, we'd probably have a clear shot. In addition there are quite a few tall trees between the location and the hills over which Sutro lies, and the hills themselves are wooded.

Using a small loop antenna on the back of the STB, we could not receive anything: the STB's own "antenna signal quality" indication, a numeric scale with 100 being theoretical post-equalizer perfection, would not even register (numbers below 20 are simply shown as "--", and pix usually won't show up much below a 40 indication).

If I picked the STB up and held it at head level, we would get a 20-22 indication -- unless I ducked my head (apparently my head, on the opposite side of the STB from Sutro Tower, made a good reflector)!

We then tried a simple dipole with a straight corner reflector (no gain). If we went outside on the back deck and laid the antenna facing in the general direction of the transmitter, we could get a level of 20-38 for most of the stations. We mounted the antenna on a six foot mast and carefully aimed it; we got levels of 35-70 and received pix from all but one transmitters. (a ten degree lateral mis-aiming was enough to kill reception).

During the two hours we watched pix, we saw a few dropouts on the marginal stations (those reading in the mid-30s on the quality scale), but the better stations came through cleanly all the time.

The CE said that this box was noticeably better than any of the 1st generation STBs he had tested, though he didn't want to make a quantitative judgement yet. He's tested it in a number of places and said that it did a much better job with multipath than the 1st gen boxes. Also, amusingly, just about every location he went to had a problem with one station or another -- usually a different one at each site, with no rhyme or reason as to which station would fail. As all the stations we were trying to pick up use co-located antennas with perhaps 100 feet of total vertical separation amongst them, this was interesting... Bear in mind that all the current 8-VSB modulators are represented in the mix of DTV signals on the air here, so that differences in receivability despite co-location may have to do the differences in the modulators and transmitters.

Channel-surfing between DTV stations in the San Carlos location with the 2nd generation box took about 1-2 seconds -- not instantaneous, but better than the 5-10 seconds seen previously.

The sound was out of sync with pix on most DTV stations, but only a little -- enough to be bothersome to the three TV engineering/production geeks in the room, but not enough that you could count the frames.

For grins, we dialed up the analog feed from a couple of the broadcasters on another monitor. The DTV feed was typically 1.5 seconds lagging behind the analog feed.

Same old content on analog and digital. The digital revolution ain't gonna fix that! :-)

Cheers, -- Adam Wilt


Subj: E Cinema
By: Craig Risebury - Telecine Product Mgr-USA Cintel Inc. >>>  <<<
Cintel has been involved with Digital Projection systems for some time now, developing electronic circuitry for Digital Projections range of projectors.  Recently however our new telecine the C-Reality has been used for film transfers for E Cinema projectors.

Test transfers and projections using various technologies have shown to the film community here in Hollywood to demonstrate the capabilities of the projectors in comparison to film.

These tests have highlights that there are differences between projector technology and the telecine transfer technology. Transferring a film for E Cinema projection is the same as creating a master in a telecine suite for subsequent duplication for general video release. Some may say that because of the very large projection screen the image quality has to be superior.

What we found with C-Reality is the projected image better matches the film projection. Why? Flying Spot Telecine technology has always been said to have that "filmic" quality and this is certainly seen on a 50 foot screen when compared to the film projection.

Filmic quality has been described in a number of ways but basically to me it is, depth of field where the image has depth to it just like film, the ability to distinguish the subtle differences in shades of black and the ability to see detail in these blacks. These can be seen with in the C-Reality film transfers as opposed to film transfers using CCD technology. The differences are quite clear.

The right projector technology and the right telecine technology will allow E Cinema projections the ability to compete with theater release prints. We will start to see electronic projection system in the theaters soon. But in order for general acceptance of electronic projection systems a number of questions need to be answered. Security and piracy. Standards need to be set to allow the theaters the ability to purchase equipment and not to have to worry about buying new equipment. Image quality on screen, due to the different technologies involved starting at the film transfer and right through to the transmission and reception and then the final projection, a system of determining image quality in the theaters need to be established.

I would have thought that the major broadcasters would be involved with the E Cinema concept and be part of the drive that is taking place. This technology in my opinion transfer over to home theater and the learning process in delivering the E Cinema concept to the theaters would be in valuable for the major broadcasters.

Craig Risebury


Subj:  More on the Electron Beam People Stopper

By: Robert Gonsett and The CGC Communicator - Communications General Corporation (CGC),  consulting radio engineers, Fallbrook, CA. >>> <<<

(Ed Note: The original story in Tech Note #36 was inspired by a story in the CGC Communicator.)

To immobilize a person, two parallel laser beams are used; one "sends" current, the other receives it (completing the circuit).  To immobilize a car, only one beam is used.  In that case, a high voltage is passed over the ionized path and the car "arcs over" to ground, completing the circuit and causing the electronic ignition to go haywire and stop working. The police car carrying the laser must drag a ground strap or its ignition would stop working too. 

Robert Gonsette

(For additional information, visit HSV Technologies, Inc.'s. Web page at WWW.N6RPF.COM-US.NET\HSV\)


Subj:   FCC Revises Local Television Ownership Rules

From: Robert Gonsett and The CGC Communicator - Communications General Corporation (CGC), consulting radio engineers, Fallbrook, CA. >>> <<<

(Ed Note: You may wish to check these out.)


Subject: More Excerpts from SCRI International's Jan., 1999 HDTV Survey

From:     Des Chaskelson, Research Director, SCRI International >>> <<<

(Ed Note: The Tech Notes staff assisted SCRI in the preparation of their original report.) 

Type of Feed

There is enough creative genius in the broadcast industry to productively generate the material for multichannel and to supplement the network feeds. PBS is the only network who, as of now, is distributing their material at 19.45 Mbps. It is difficult, at best, to determine what equipment to buy, or produce, if the dust has not settled nor the decision on standards of network distribution have not been reached. 45.6 percent of the TV Stations surveyed bear this out. Only then can the various necessary and familiar devices for in-station support of feeds for such things as ID's, supers, EAS, etc., be developed.

This notwithstanding, 31% of stations expect to use pass through (19.4Mbps), while 24% expect to use network contribution feeds (40-60 Mbps).

Inserting Logos, CGs into HD Signal with Pass-Through Feed

As with many issues relating to DTV implementation, there is a great deal of uncertainty regarding how those stations relying on a pass-through feed will be able to insert things like the watermark or "bug" in the lower right hand corner of the picture of their digital network feeds. This is reflected in the numbers where more than half (53.2%) do not know how they will do this. About one in five stations (19.2%) expect to decode part of the signal and insert into that portion; about in ten (9.4%) expect to decode the entire 19.4 Mbps signal; and less than one ten (7.9%) expect to have the network insert the logo. Probably the most important of the keys is the EAS information so vital to many communities. The answer to this may well be to have a device that will do the downstream keying in the digital domain. There are some out there in the experimental stages of development and we can expect more to come.

Des Chaskelson


The Tech Notes are published for broadcast professionals, and others, who are interested in Electronic Cinema, DTV, etc., by Larry Bloomfield and Jim Mendrala.  We can be reached by either e-mail or land lines (408) 778-3412, (661) 294-1049 or fax at (661) 294-0705. The Tech Notes are sent (BCC) directly only to those who have asked to be on the mailing list, however feel free to forward them, intact, to anyone who you think might be interested.  There is no charge for this Newsletter, no one gets paid (sigh), there is no advertising and we do not indorse any product or service(s).  The ideas and opinions are those of the individual authors.  We still administer everything manually.  We don't use any "majordomo" automatic servers. News items, comments, observations, opinions, etc., are encouraged and always welcome. We publish when there is something to share.  Material may be edited for brevity, but usually not.  Tech Note articles may be reproduced in any form provided they are unaltered and credit is given to both Tech Notes and the originating authors, when named.  If they are to be used by a publication that normally compensates their writers, please contact us first.